Search: id:A103314
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%I A103314
%S A103314 1,1,2,2,4,2,10,2,16,8,34,2,100,2,130,38,256,2,1000,2,1156,134,2050,2,
%T A103314 10000,32,8194,512,16900,2,146854,2,65536,2054,131074,158,1000000,2,
%U A103314 524290,8198,1336336,2,11680390,2,4202500,54872,8388610,2,100000000,128
%N A103314 Total number of subsets of the n-th roots of 1 that add to zero.
%C A103314 The term a(0) = 1 counts the single zero-sum subset of the (by convention) 
               empty set of zeroth roots of 1.
%C A103314 Comment from David W. Wilson, May 19 2005: I am inclined to believe that 
               if S is a zero-sum subset of the n-th roots of 1, that n can be built 
               up from (zero-sum) cyclically balanced subsets via the following 
               operations: 1. A U B, where A and B are disjoint. 2. A - B, where 
               B is a subset of A.
%C A103314 Lam and Leung's paper, though interesting, does not apply directly to 
               this sequence because it allows repetitions of the roots in the sums.
%C A103314 Observe that 2^n=a(n) (mod n). Sequence A107847 is the quotient (2^n-a(n))/
               n. - T. D. Noe (noe(AT)sspectra.com), May 25 2005
%C A103314 Comment from Max Alekseyev, Jan 31 2008 (Start): Every subset of the 
               set U(n) = { 1=r^0, r^1, ..., r^(n-1) } of the n-th power roots of 
               1 (where r is a fixed primitive root) defines a binary word w of 
               the length n where the j-th bit is 1 iff the root r^j is included 
               in the subset.
%C A103314 If d is the period of w with respect to cyclic rotations (thus d|n) then 
               the periodic part of w uniquely defines some binary Lyndon word of 
               the length d (see A001037). In turn, each binary Lyndon word of the 
               length d, where d<n and d|n, corresponds to d distinct zero-sum subsets 
               of U(n).
%C A103314 The binary Lyndon words of the length n are different in this respect: 
               only some of them correspond to n distinct zero-sum subsets of U(n) 
               while the others do not correspond to such subsets at all. A110981(n) 
               gives the number of binary Lyndon words of the length n that correspond 
               to zero-sum subsets of U(n). (End)
%H A103314 Max Alekseyev and M. F. Hasler, <a href="b103314.txt">Table of n, a(n) 
               for n = 0..164</a>
%H A103314 T. Y. Lam and K. H. Leung, <a href="http://arXiv.org/abs/math.NT/9511209">
               On vanishing sums for roots of unity</a>
%H A103314 T. D. Noe, <a href="http://www.sspectra.com/math/RootSums.html">Sums 
               of Roots of Unity Plots</a>
%H A103314 T. D. Noe, <a href="http://www.sspectra.com/math/A103314-Proof.pdf">Proof 
               a(n)=a(s(n))^(n/ s(n))</a>
%H A103314 Sasha Rybak, in: <a href="http://lib.mexmat.ru/forum/viewtopic.php?p=78783#78783">
               Zero sums of roots of unity</a> on forum.mexmat.ru.
%F A103314 a(n) = A070894(n)+1.
%F A103314 a(2^n) = 2^(2^(n-1)). - Dan Asimov and Gareth McCaughan, Mar 11 2005
%F A103314 a(2n) = a(n)^2 if n is even. If p, q are primes, a(pq) = 2^p+2^q-2. In 
               particular, if p is prime, a(2p) = 2^p + 2. - Gareth McCaughan, Mar 
               12 2005
%F A103314 a(n) == 2^n (mod n), a(p) = 2 (p prime). - David W. Wilson (davidwwilson(AT)comcast.net), 
               May 08 2005
%F A103314 It appears that a(n) = a(s(n))^(n/s(n)) where s(n) = A007947(n) is the 
               squarefree kernel of n. This is true if all zero-sum subsets of the 
               n-th roots of 1 are formed by set operations on cyclic subsets. If 
               true, A103314 is determined by its values on squarefree numbers (A005117). 
               Some consequences would be a(p^n) = 2^p^(n-1), a(p^m q^n) = (2^p+2^q+2)^(p^(m-1) 
               q^(n-1)) and a(p^2 n) = a(pn)^p for primes p and q. - David W. Wilson 
               (davidwwilson(AT)comcast.net), May 08 2005
%F A103314 a(pn) = a(n)^p when p is prime and p|n; a(2p) = 2^p+2 when p is an odd 
               prime. More generally a(pq) = 2^p+2^q-2 when p, q are distinct primes. 
               - Gareth McCaughan (gareth.mccaughan(AT)pobox.com), Mar 12 2005
%F A103314 For distinct odd primes p and q, a(2pq) = (2^p+2)^q + (2^q+2)^p - 2(2^p+1)^q 
               - 2(2^q+1)^p + 2^(pq) + SUM[j=0..p] binomial(p,j)(2^j+2^(p-j))^q. 
               - Sasha Rybak, Sep 21 2007.
%F A103314 a(n) = n*A110981(n) + 2^n - n*A001037(n). - Max Alekseyev, Jan 14 2008
%t A103314 Table[Plus@@Table[Count[(KSubsets[Range[n], k]), q_List/;Chop[Abs[Plus@@(E^(2.*Pi*I*q/
               n))]]==0], {k, 0, n}], {n, 15}] (T. D. Noe)
%t A103314 Needs["DiscreteMath`Combinatorica`"]; Table[Plus@@Table[Count[(KSubsets[Range[n], 
               k]), q_List/;Chop[Abs[Plus@@(E^(2.*Pi*I*q/n))]]==0], {k, 0, n}], 
               {n, 15}] (T. D. Noe)
%o A103314 (PARI program from Max Alekseyev and M. F. Hasler that implements all 
               known results, Jan 31 2008)
%o A103314 /* works for all n except for 165, 195, 210, 231, 255, 273, 285, 330, 
               345, ... */
%o A103314 A103314(n) = { local(f=factor(n)); n<2 & return(1); n==f[1,1] & return(2);
%o A103314 vecmax(f[,2])>1 & return(A103314(f=prod(i=1,#f~,f[i,1]))^(n/f));
%o A103314 if( 2==#f=f[,1], return(2^f[1]+2^f[2]-2));
%o A103314 #f==3 & f[1]==2 & return(sum(j=0,f[2],binomial(f[2],j)*(2^j+2^(f[2]-j))^f[3])
%o A103314 +(2^f[2]+2)^f[3]+(2^f[3]+2)^f[2]-2*((2^f[2]+1)^f[3]+(2^f[3]+1)^f[2])+2^(f[2]*f[3]));
%o A103314 n==105 & return(166093023482); error("A103314(n) is unknown for n=",n) 
               }
%Y A103314 Equals A070894 + 1. A107847(n) = (2^n - A103314(n))/n, A110981 = A001037 
               - A107847.
%Y A103314 Row sums of A103306. See also A006533, A006561, A006600, A007569, A007678.
%Y A103314 Cf. A070925, A107753 (number of primitive subsets of the n-th roots of 
               unity summing to zero), A107754 (number of subsets of the n-th roots 
               of unity summing to one), A107861 (number of unique values in the 
               sums of all subsets of the n-th roots of unity).
%Y A103314 Sequence in context: A103178 A087909 A076078 this_sequence A111741 A111793 
               A064482
%Y A103314 Adjacent sequences: A103311 A103312 A103313 this_sequence A103315 A103316 
               A103317
%K A103314 nonn,nice,hard
%O A103314 0,3
%A A103314 Wouter Meeussen (wouter.meeussen(AT)pandora.be), Mar 11 2005
%E A103314 More terms from David W. Wilson, Mar 12, 2005
%E A103314 Scott Huddleston (scotth(AT)ichips.intel.com) finds that a(30) >= 146854 
               and conjectures that is the true value of a(30). - Mar 24 2005. Confirmed 
               by Meeussen and Wilson.
%E A103314 More terms from T. D. Noe (noe(AT)sspectra.com), May 25 2005
%E A103314 Further terms from Max Alekseyev (maxale(AT)gmail.com) and M. F. Hasler 
               (Maximilian.Hasler(AT)gmail.com), Jan 07 2008
%E A103314 Edited by M. F. Hasler (Maximilian.Hasler(AT)gmail.com), Feb 06 2008

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